1. Field of the Invention
The present invention relates to a picture processing apparatus, a picture processing method adopted by the picture processing apparatus, a picture processing method program implementing the picture processing method and a recording medium used for recording the picture processing method program. For example, the embodiments of the present invention can be applied to a stream decoding apparatus capable of decoding an MPEG (Moving Picture Experts Group)-2 bit stream and an MPEG-4 Part10 AVC (Advanced Video Coding) bit stream which is referred to as an H.264/AVC bit stream in the following description. In comparison with the existing technology, a technology according to the embodiments of the present invention are capable of effectively avoiding deteriorations of the quality of a picture with a high degree of reliability by making use of a simple configuration. This is because, as will be described later in detail, the embodiments of the present invention set boundary-strength determination information in accordance with whether an intra coding process or an inter coding process has been carried out on adjacent predicted-value generation units and in accordance with whether or not a boundary between adjacent orthogonal transform process units coincides with a boundary between the predicted-value generation units and, if prediction modes for generating predicted values in the adjacent orthogonal transform process units are different from each other, the boundary-strength determination information is set so that the strength of a filtering process becomes large in comparison with a case in which the adjacent orthogonal transform process units have the same prediction mode.
2. Description of the Related Art
The existing video apparatus carries out data compression/coding processing on moving pictures by adoption of a compression technique such as the MPEG (Moving Picture Experts Group)-2 or H.264/AVC coding/decoding method. In this patent specification, the data compression/coding processing is also referred to simply as coding processing. An MPEG-2 coding apparatus serving as an existing video apparatus adopting the MPEG-2 coding/decoding method delimits successive pictures into GOP (group of pictures) units, sets types for pictures included in each of the GOP units and rearranges the pictures in the GOP unit. In addition, the MPEG-2 coding apparatus delimits the rearranged pictures into macroblock units, each of which is used as the predicted-value generation unit cited above, and generates a prediction error, which is a difference between the true value of a macroblock unit and a predicted value according to the type of the picture, for each of the macroblock units. Subsequently, the MPEG-2 coding apparatus carries out a DCT (Discrete Cosine Transform) process on the prediction errors of the macroblock units in DCT block units, each of which is the aforementioned orthogonal transform process unit having a size of 8 pixels×8 pixels, to result in DCT coefficients. Then, the MPEG-2 coding apparatus carries out a sequential quantization process and an entropy coding process on the DCT coefficients in order to generate a bit stream.
In order to be compatible with the MPEG-2 coding apparatus having the configuration described above, an MPEG-2 decoding apparatus 1 for carrying out data decompression/decoding processing on an MPEG-2 bit stream S1 generated by the MPEG-2 coding apparatus is designed to have a configuration shown in a block diagram of FIG. 21. In this patent specification, the data decompression/decoding processing is also referred to simply as decoding processing. In the MPEG-2 decoding apparatus 1, an entropy decoding section 2 receives an MPEG-2 bit stream S1 and carries out an entropy decoding process as a part of the decoding processing, which is being carried out by the MPEG-2 decoding apparatus 1, on the MPEG-2 bit stream S1. A motion prediction section 3 detects a motion vector MV from data output by the entropy decoding section 2 and supplies the motion vector MV to a motion compensation section 4. The motion compensation section 4 carries out a motion compensation process on reference picture data stored in an FM (frame memory) 5 by making use of the motion vector MV received from the motion prediction section 3 in order to generate a predicted value corresponding to an inter coding process carried out previously by a coding apparatus to generate the MPEG-2 bit stream S1. An intra prediction section 6 to be described more later is a section for generating a predicted value corresponding to an intra coding process, which has been carried out by the coding apparatus to generate the MPEG-2 bit stream S1, on the basis of data output by an addition section 9 also to be described more later.
An inverse quantization (IQ) section 7 carries out an inverse quantization process as a part of the decoding processing, which is being carried out by the MPEG-2 decoding apparatus 1, on data output by the entropy decoding section 2 in order to generate a DCT (Discrete Cosine Transform) coefficient. The DCT coefficient is the same data as the DCT coefficient generated in the course of the coding process carried out by the MPEG-2 coding apparatus as described above. An inverse DCT transform section 8 carries out an inverse DCT process as a part of the decoding processing, which is being carried out by the MPEG-2 decoding apparatus 1, on the DCT coefficient output by the inverse quantization section 7 in order to generate a prediction error. The prediction error is the same data as the prediction error generated in the course of the coding process carried out by the MPEG-2 coding apparatus as described above. The addition section 9 cited above carries out an addition process as a part of the decoding processing, which is being carried out by the MPEG-2 decoding apparatus 1, to add a predicted value output by the motion compensation section 4 or the intra prediction section 6 to the prediction error generated by the inverse DCT transform section 8 in order to generate picture data for each macroblock. The addition section 9 outputs the picture data to the intra prediction section 6. In the MPEG-2 decoding apparatus 1, the picture data generated by the addition section 9 is stored in the frame memory 5 on a temporary basis. Then, pictures of the picture data stored in the frame memory 5 are rearranged in order to produce a video signal SV. In addition, the picture data stored in the frame memory 5 is also used as the aforementioned reference picture data supplied to the motion compensation section 4.
In the same way as the MPEG-2 coding/decoding method, in accordance with the H.264/AVC coding/decoding method, prediction errors found by carrying out intra prediction and inter prediction processes are subjected to orthogonal transform and variable-length coding processes in order to compress a moving picture. The H.264/AVC coding/decoding method is different from the data MPEG-2 coding/decoding method in that, in the case of the H.264/AVC coding/decoding method, a variety of devices are contrived so that the coding process to compress data can be carried out with an even higher degree of efficiency.
FIG. 22 is a block diagram showing an H.264/AVC decoding apparatus 11 to be compared with the MPEG-2 decoding apparatus shown in the block diagram of FIG. 21. In the H.264/AVC decoding apparatus 11, an entropy decoding section 12 receives an H.264/AVC bit stream S2 and carries out an entropy decoding process as a part of the decoding processing, which is being carried out by the H.264/AVC decoding apparatus 11, on the H.264/AVC bit stream S2. A motion prediction section 13 detects information such as a motion vector MV and information used for identifying a reference frame from data output by the entropy decoding section 12 and supplies the detected information to a motion compensation section 14. The motion compensation section 14 carries out a motion compensation process on reference picture data stored in an FM (frame memory) 15 by making use of the information received from the motion prediction section 13 in order to generate a predicted value corresponding to an inter coding process carried out by a coding apparatus to generate the H.264/AVC bit stream S2. As described above, the information received from the motion prediction section 13 includes a motion vector MV. An intra prediction section 16 to be described more later is a section for generating a predicted value corresponding to an intra coding process, which has been carried out by the coding apparatus to generate the H.264/AVC bit stream S2, on the basis of data output by an addition section 19 also to be described more later.
An inverse quantization (IQ) section 17 carries out an inverse quantization process as a part of the decoding processing, which is being carried out by the H.264/AVC decoding apparatus 11, on data output by the entropy decoding section 12 in order to generate a DCT (Discrete Cosine Transform) coefficient. The DCT coefficient is the same data as the DCT coefficient generated in the course of the coding process carried out by an H.264/AVC coding apparatus. An inverse DCT transform section 18 carries out an inverse DCT process as a part of the decoding processing, which is being carried out by the H.264/AVC decoding apparatus 11, on the DCT coefficient output by the inverse quantization section 17 in order to generate a prediction error. The prediction error is the same data as the prediction error generated in the course of the coding process carried out by the H.264/AVC coding apparatus. The addition section 19 cited above carries out an addition process as a part of the decoding processing, which is being carried out by the H.264/AVC decoding apparatus 11, to add a predicted value output by the motion compensation section 14 or the intra prediction section 16 to the prediction error generated by the inverse DCT transform section 18 in order to generate picture data. The addition section 19 outputs the picture data to the intra prediction section 16 and a deblocking filter 20.
A deblocking filter 20 removes block noises from the picture data generated by the addition section 19. In the H.264/AVC decoding apparatus 11, picture data generated by the deblocking filter 20 is stored in the frame memory 15 on a temporary basis. Then, pictures of the picture data stored in the frame memory 15 are rearranged in order to produce a video signal SV. In addition, the picture data stored in the frame memory 15 is also used as the aforementioned reference picture data supplied to the motion compensation section 14.
In the coding processing adopting the MPEG-2 or H.264/AVC coding/decoding method, if the data compression rate is increased, high-frequency components are lost in the quantization process. As a result, gradation differences are generated on boundaries between DCT blocks of the video signal SV obtained as a result of the decoding processing. In addition, in the case of a vigorous motion or the like, the prediction error also increases. As a result, high-frequency components are also lost as well in the quantization process and, thus, gradation differences are generated on boundaries between DCT blocks of the video signal SV obtained as a result of the decoding processing. On top of that, in the case of a vigorous motion, the prediction error in the macroblock also increases and, as a result, gradation differences are generated on boundaries between macroblocks. The gradation differences generated on the boundaries between DCT blocks and on the boundaries between macroblocks due to lost high-frequency components substantially deteriorate the quality of the picture. The gradation differences generated on the boundaries between DCT blocks and on the boundaries between macroblocks are referred to as block noises.
In the case of the H.264/AVC coding/decoding method, the use of a deblocking filter is prescribed. The deblocking filter is a filter for repressing the block noises. In the case of the MPEG-2 coding/decoding method, however, the use of a deblocking filter is not prescribed. Thus, in order to repress the block noises in the case of the MPEG-2 coding/decoding method, a block-noise reduction apparatus 21 is newly added to the MPEG-2 decoding apparatus 1 shown in the block diagram of FIG. 21 and provided at the output stage of the MPEG-2 decoding apparatus 1 to give a configuration shown in a block diagram of FIG. 23. The block-noise reduction apparatus 21 is an apparatus for repressing the block noises of the video signal SV. It is to be noted that, in the configuration shown in the block diagram of FIG. 23, components identical with their respective counterparts employed in the MPEG-2 decoding apparatus 1 shown in the block diagram of FIG. 21 are denoted by the same reference numerals as the counterparts and the explanation of the identical components is omitted in order to avoid duplications of descriptions.
With regard to the decoding processing adopting the MPEG-2 coding/decoding method or the like, each of Japanese Patent Laid-Open No. 2007-184870 and Japanese Patent Laid-Open No. 2007-184871 discloses a configuration omitting the process carried out by the deblocking filter, depending on a coding mode and a quantization parameter. Japanese Patent Laid-Open No. 2007-36463 discloses a configuration making use of a deblocking filter provided for the H.264/AVC data decompression/decoding apparatus in an MPEG-2 data decompression/decoding apparatus. In this patent specification, the data decompression/decoding apparatus is also referred to simply as a decoding apparatus and, by the same token, a data compression/coding apparatus is also referred to simply as a coding apparatus. In this patent specification, the decoding apparatus and the coding apparatus are also referred to as the aforementioned picture processing apparatus, which is a generic technical term provided for both the decoding apparatus and the coding apparatus.
Incidentally, in order to repress block noises so as to effectively prevent the picture quality of the video signal SV from deteriorating by making use of the block-noise reduction apparatus 21 provided at the output stage of the MPEG-2 decoding apparatus 1 as shown in the block diagram of FIG. 23, it is necessary to selectively repress merely gradation differences caused by the block noises. It is thus necessary to detect merely block-noise components from a base-band video signal with a high degree of reliability so that, in consequence, there is raised a problem of a complicated overall configuration.
As a method for solving this problem, it is conceivable to apply a technique described in Japanese Patent Laid-Open No. 2007-36463. In particular, a decoding apparatus configured to be capable of decoding both the MPEG-2 and H.264/AVC bit streams is forecasted in recent years. Thus, if the deblocking filter used in the H.264/AVC decoding apparatus can be used in the MPEG-2 decoding apparatus, the configuration of the decoding apparatus configured to be capable of decoding both the MPEG-2 and H.264/AVC bit streams can be made even simpler.
Because of existence of various processes not described by the H.264/AVC specifications as processed for the MPEG-2 coding/decoding method, however, the technique disclosed in Japanese Patent Laid-Open No. 2007-36463 raises a problem of inadequacies still existing in the practical use.